Carburetor



Sept. 19, 1967 TAsuKU DATE ETAL CARBURETOR 2 Sheets-Sheet 1 Filed Feb. ll, 1966 ilu 2 /9/6 ILYIIIIIIIII' lll l ma.

SePt- 19, 1967 TAsUKU DATE ETAL 3,342,463

CARBURETOR 2 Sheets-Sheet 2 Filed Feb'. l1, 1966 United States Patent O 3,342,463 CARBURETQR Tasuku Date and' Ryuzo Kajikawa, Tokyo, Japan, assignors to Kabusiriki Kasha Honda Gijutsu Kenkyusho, Saitama-ken, `lapan Filed Feb. 11, 1966, Ser. No. 526,733 Claims priority, application Japan, Feb. 20, 1965, 40/ 9,351 6 Claims. (Cl. 261-44) ABSTRACT F THE DISCLOSURE A carburetor in which a spring loaded piston is subjected to the suction pressure in the venturi such that at high engine speed the piston is urged into the venturi against the action of its spring to block the air ow and diminish engine output. A needle is mounted on the piston and is inserted in increasing amounts into a main fuel nozzle as the piston moves into the venturi whereby the quantity of fuel injected into the venturi is reduced thereby further diminishing engine output.

The present invention relates to a carburetor for use with an internal combustion engine for a vehicle.

It is a principal object of the invention to provide such a carburetor in which the engine speed, and thereby the vehicle speed is automatically limited so as not to increase excessively, regardless of throttle control, while at the same time leaving the acceleration performance at loW speed unaffected.

According to the present invention, there is provided in the carburetor an air passage with a venturi and a manually operable throttle valve disposed in said air passage at its engine side. According to a first characteristic feature of the invention there is provided a movable member which is displaceable into the venturi so that when the negative pressure at or near the venturi reaches a predetermined value, the movable member is acted on by said negative pressure to reduce the size of the venturi, said movable member being provided with a fuel control mechanism for controlling the amount of fuel injected intoV the venturi.

According to a second feature of the invention, a negative pressure flow passage is provided between the throttle valve and the venturi, so that even when the throttle valve is in a throttle position, the movable member may be operated by the negative pressure of the air rapidly passing the throttle valve, whereby excessive increase of speed can be effectively limited even when the vehicle running resistance is small such as when it descends a hill.

An embodiment of a carburetor according to the present invention will next be described with reference to the drawings; in which:

FIGURE 1 is a longitudinal sectional side view of a carburetor according to the present invention;

FIGURE 2 is a longitudinal sectional side View of a portion of the carburetor of FIGUREI showing the condition where a movable member is in operative state; and

FIGURE 3 is a speed-output diagram explaining the performance of the carburetor according to the present invention.

ICC

In the drawing numeral 1 denotes a Ventilating tube of a carburetor, having an air passage 2 therein which is slightly narrowed in a portion thereof to form a venturi 3. A throttle valve 4 is supported in the air passage 2 in front of the venturi, that is, on the engine side of the carburetor and a choke valve 5 is provided at the rear side thereof. The tube 1 is provided at its venturi 3 with a tubular wall 6 projecting outwardly, and a piston 7 is mounted slidably therein. A screw rod 9 connected to a supporting rod 8 xed to the piston 7 has inner and outer washers 1d and 11 mounted thereon, and the central portion of a diaphragm 12 is held therebetween. A balance spring 13 encircles tubular wall 6 and acts on the inner washer 10 to urge the same outwards. A nut 14 is mounted on rod 9 to retain the washers 10 and 11 on the rod 9. Integral with tube 1 is an annular wall 15 surrounding the piston 7, and a circumferential portion of the diaphragm 12 is held between the wall 15 and a cover 16 therefor. A head portion 9A of said screw rod 9 is urged by the balance spring 13 into contact under pressure with the inner surface of the cover 16. A chamber defined by the annular wall 15 and the cover 16 is divided by the diaphragm 13 into an inner chamber 17 and an outer chamber 19. The inner chamber becomes subjected to negative pressure by being in communication with a passage 18 which opens into venturi 3, while the outer chamber is subjected to normal pressure by being in communication with the intake side of the air passage 2 through an air passage 20. Alternatively, chamber 19 can be open to the atmosphere. Numeral 21 is a tapered needle projecting from the inner surface of the piston 7. Numeral 22 is a main fuel nozzle into which the jet needle 21 is inserted. Numerals 23 and 24 are a main jet and an air bleed for the main nozzle, and numeral 25 is a fuel nozzle for slow speed or idle of the engine disposed near the throttle valve 4. Numerals 26 and 27 are a jet and an air bleed for the idle nozzle 25. Numeral 28 is a iioat chamber and numeral 29 is a float, these being of conventional construction.

If, in the hitherto known conventional carburetors, the engine speed (r.p.m.), and thereby, the vehicle running speed is desired to be automatically controlled so as not to increase excessively, the venturi is usually small in diameter or if the venturi is large in diameter, the throttle valve is limited in its degree of opening, so that when the engine speed is increased to high values the quantity of suction air is decreased to limit the output power of the engine. With such a constructi-on as above, however, the quantity of suction air at low speeds is also decreased so that the torque is decreased and the acceleration performance of the engine is adversely affected.

The present invention is free from the above deficiency, and the venturi 3 can be made large in diameter and the throttle valve 4 can be opened fully.

The operation of the carburetor of the invention will be explained as follows:

In FIG. 1 the throttle valve 4 is open only to a slight degree and the engine is operating at low speed.

In this case, the quantity of flow of the suction air at the venturi 3 is small, and thus the negative pressure thereat is low. Accordingly, the negative pressure within the chamber 17 does not overcome the strength of the balance spring 13, so that the piston 7 is maintained in its retracted condition as shown in FIG. 1. Then, if the throttle valve 4 is opened to a large magnitude or opened fully to accelerate the engine, the amount of air flowing in the venturi 3 is increased in accordance with the opening of the throttle valve, and the negative pressure in the chamber 17 is also increased. During the time when the engine speed is increasing but has not reached a limit speed, the balance spring 13 overcomes the negative pressure in the chamber 17 and the piston 7 is not operated and remains retracted. If, in such case, the throttle valve 4 is fully opened, excellent acceleration performance can be obtained because the venturi 3 has not been restricted in diameter. It, then, the engine speed begins to reach the limit speed, the negative pressure within the chamber 17 increases and finally the pressure acting on the diaphragm 12 overcomes the force of the balance spring 13 to compress the same as shown in FIG. 2, and cause the piston 7 to project into the venturi 3 to decrease the size of the venturi and the quantity of air flow, while at the same time the jet needle 21 penetrates more deeply into the main fuel nozzle 22 to decrease the flow of the fuel into the venturi. Accordingly, the engine output power is decreased, and the acceleration of the engine, and thereby of the vehicle is terminated when the output power reaches a balance with the vehicle running resistance, whereby the vehicle speed is limited to that point. The projecting speed, in this case, of the piston 7 into the venturi 3 is very rapid for the following reason. Namely, once the piston 7 begins to project into the venturi, the latter becomes reduced in size and the quantity of air flow is decreased, however, the air speed is increased to increase the negative pressure, so that the projecting speed of the piston 7 is further promoted thereby.

The above operation will be explained further with reference to the speed-output diagram of FlG. 3 wherein:

A shows the engine speed, and thereby the vehicle running speed as compared to the engine power output, and B shows the starting point of the operation of the piston 7. The curve A goes down sharply as shown by curve C beyond the point B. If the curve C intersects a speedrunning resistance curve D at O, the speed is so limited that the speed corresponding to the point O is a maximum. Curve E shows the speed-output curve in the case where the venturi is made small in diameter or where the throttle is limited so as not to be fully operable. It is to be noted that the curve E is below the curve A showing that the acceleration performance at low speeds is greatly inferior to that of the engine with the carburetor of the present invention. Curve F is the speed-output curve in the case where the movable venturi member, that is, the piston 7 is eliminated from the carburetor of FIG, l and the throttle valve 4 is opened fully, and it shows that in this case the speed is excessively increased beyond the desired restricted Value at 0.

Thus, the carburetor according to the present invention is advantageous in that the acceleration performance, at the time when the engine speed, that is, the vehicle running speed is low, is not affected and excessive increase in the speed can be automatically controlled. Additionally, the construction of the carburetor according to the invention is simple.

Although there has been illustrated in the drawing an arrangement wherein in order to make the venturi variable, the piston 7 is used, the same can be changed to a diaphragm or the like.

In the case where the vehicle running resistance is small, that is, in the case where, for example, the vehicle descends a slope, the driver partially closes the throttle valve to decrease the air ow, so that the piston 7 does not operate satisfactorily even if the speed is excessively increased with the above construction alone.

A second characteristic feature of the invention is to remove this defect.

For this purpose there is shown in FIG. l a passage 30 in communication with chamber 17 and opening into passage 2 between the venturi 3 and the throttle valve 4. Passage 39 serves to intake a large negative pressure caused by rapid air flow passing through a narrow air gap 31 at the time when the throttle valve 4 is in partially closed position. Thus, even if the throttle 4 is partially closed, the piston 7 will operate effectively at near the desired speed. Since, in this case, the negative pressure of the venturi 3 is small, the passing air partly ows in reverse into the chamber 17 through the negative pressure passage 18 to prevent the increase of the negative pressure within the chamber 17. However, the influence by this reverse ow can be substantially removed if the inner diameters of the negative pressure passages 18, 30, and the tension force of the balance spring 13 are properly selected. For this purpose, an adjusting projection member 32 is disposed in tube 1 for adjusting the resistance to air flow through the passage 30.

By moving the negative pressure passage 30 to a position near the venturi 3, the negative pressure passage 18 can even be omitted, so that by use of a single negative pressure passage 30 alone, the piston 7 can be operated regardless of the magnitude of the running resistance.

Numerous modifications and variations of the disclosed invention will become apparent to those skilled in the art without departing from the scope and spirit of the invention as defined in the attached claims.

What we claim is:

1. A carburetor having an air passage with a reduced portion therein forming a venturi, said carburetor comprising a manually operable throttle valve in said passage on one side of the Venturi for controlling air flow through said passage, means at said venturi for the injection of fuel in the air passage in response to the development of negative pressure at said venturi due to air flow through said passage, and means adjacent said passage at said venturi to both reduce the size of the venturi and cooperate with the fuel injection means to adjust the quantity of fuel injected into the venturi all in response to a predetermined negative pressure in the passage, the latter means comprising first means for projecting into the venturi in response to said negative pressure, second means extending from said rst means for acting on said fuel injection means to regulate the quantity of fuel injected in relation to the magnitude of projection of the first means into the venturi, a chamber opening into said passage, means subjected to the pressure in said chamber and acting on said first means, and biassing means acting on said first means to urge the same to an initial retracted position in which the first means has no affect on the air and fuel flow in said passage, said biassing means having a particular strength which is overcome when the negative pressure in said chamber reaches a value corresponding to said predetermined negative pressure in the passage.

2. A carburetor as claimed in claim 1 wherein said chamber opens into said passage at two locations one being at the venturi, the other being between the venturi and the throttle valve.

3. A carburetor as claimed in claim 1, wherein fuel injection means comprises a main fuel nozzle at said venturi opening thereinto, said second means comprising a needle extending from said first means into said main fuel nozzle to penetrate and block the same in increasing amounts as the tirst means is projected into the passage.

4. A carburetor as claimed in claim 1 wherein said chamber opens into said passage at a location between the venturi and the throttle Valve whereby with the throttle valve in throttled position said first means will be operated by the negative pressure of the air rapidly passing the throttle valve.

S. A carburetor as claimed in claim 4 wherein said means to reduce the size of the venturi and to adjust the quantity of fuel injected further comprises means defining a second chamber adjacent the rst chamber and an elastic diaphragm separating said chambers, said second chamber being exposed to atmospheric pressure, said diaphragm being coupled to said means which acts on the first means to displace the rst means against the action of the biassing means when the negative pressure in said rst chamber reaches said value corresponding to the predetermined negative pressure in the passage.

6. A carburetor as claimed in claim 5, wherein said rst means is a piston adjacent said passage supported for sliding movement into and out of said passage, said biassing means acting on the piston to urge the same to said retracted position, said diaphragm being coupled to the piston to cause displacement thereof when the negative pressure in the said rst chamber reaches said value corresponding to the predetermined negative pressure in the passage.

References Cited UNITED STATES PATENTS FOREIGN PATENTS 2/ 1906 Great Britain.

HARRY B. THORNTON, Primary Examiner.

15 TIM R. MILES, Examiner. 

1. A CARBURETOR HAVING AN AIR PASSAGE WITH A REDUCED PORTION THEREIN FORMING A VENTURI, SAID CARBURETOR COMPRISING A MANUALLY OPERABLE THROTTLE VALVE IN SAID PASSAGE ON ONE SIDE OF THE VENTURI FOR CONTROLLING AIR FLOW THROUGH SAID PASSAGE, MEANS AT SAID VENTURI FOR THE INJECTION OF FUEL IN THE AIR PASSAGE IN RESPONSE TO THE DEVELOPMENT OF NEGATIVE PRESSURE AT SAID VENTURI DUE TO AIR FLOW THROUGH SAID PASSAGE, AND MEANS ADJACENT SAID PASSAGE AT SAID VENTURI TO BOTH REDUCE THE SIZE OF THE VENTURI AND COOPERATE WITH THE FUEL INJECTION MEANS TO ADJUST THE QUANTITY OF FUEL INJECTED INTO THE VENTURI ALL IN RESPONSE TO A PREDETERMINED NEGATIVE PRESSURE IN THE PASSAGE, THE LATTER MEANS COMPRISING FIRST MEANS FOR PROJECTING INTO THE VENTURI IN RESPONSE TO SAID NEGATIVE PRESSURE, SECOND MEANS EXTENDING FROM SAID FIRST MEANS FOR ACTING ON SAID FUEL INJECTION MEANS TO REGULATE THE QUANTITY OF FUEL INJECTED IN RELATION TO THE MAGNITUDE OF PROJECTION OF THE FIRST MEANS INTO THE VENTURI, A CHAMBER OPENING INTO SAID PASSAGE, MEANS SUBJECTED TO THE PRESSURE IN SAID CHAMBER AND ACTING ON SAID FIRST MEANS, AND BIASSING MEANS ACTING ON SAID FIRST MEANS TO URGE THE SAME TO AN INITIAL RETRACTED POSITION IN WHICH THE FIRST MEANS HAS NO AFFECT ON THE AIR AND FUEL FLOW IN SAID PASSAGE, SAID BIASSING MEANS HAVING A PARTICULAR STRENGTH WHICH IS OVERCOME WHEN THE NEGATIVE PRESSURE IN SAID CHAMBER REACHES A VALUE CORRESPONDING TO SAID PREDETERMINED NEGATIVE PRESSURE IN THE PASSAGE. 